1. Field of the Invention
The present invention relates to a piston, for an internal-combustion engine, provided with a composite fiber reinforcement.
2. Description of the Related Art
In an internal-combustion engine, there has been a problem in that seizure of the piston is attributable to an excessive decrease in the clearance between the piston and the cylinder wall, resulting from thermal expansion of the piston at a high operation temperature. Although a large basic clearance between the piston and the cylinder wall serves to obviate the seizure of the piston, this gives rise to another problem, i.e., an enhancement of the noise of the internal-combustion engine during the initial period of operation after starting. To solve these problems, a strut made of a steel plate, which has a smaller thermal expansion than aluminum alloy, may be incorporated integrally into a piston when casting the same, to suppress thermal expansion of the cast piston. However, since the specific gravity of steel is greater than that of aluminum alloy, the steel strut increases the weight of the piston, which adversely affects any improvement of the performance of the internal-combustion engine. Furthermore, an internal-combustion engine having a higher performance has a tendency to operate at a higher piston temperature and, therefore, in such a high-performance engine, even a steel strut is unable to satisfactorily suppress the thermal expansion of the piston.
To solve the problems resulting from the decrease in the clearance between the piston and the cylinder wall, several techniques have been proposed. For example, the employment of a spacer expander to piston rings (Japanese Unexamined Utility Model Publication (Kokai) Nos. 56-85048 and 56-85049), and dividing a piston into a head section and a skirt section and fitting an insert in the skirt section (Japanese Utility Model Publication (Kokai) No. 58-191350) have been proposed.